If you want to contribute please follow this guideline.
For editing fxml files, use the "JavaFX Scene Builder" in version 8.5.0.
Layouting is generally done with fxml files.
For fontawesome support add Libraries
de.jensd:fontawsomefx-commons:8.15
de.jensd:fontawsomefx-fontawsome:4.7.0-5
to the "JavaFX Scene Builder"
Scene Builder may sometimes delete unicode Charakters when fxml file is changed. reset Glyph Name to reset uniocode Charakter.